Simulate fire (quick way)
You may fake a fire effect using animated movie e.g. .avi or .mov (.gifs are not supported as @Mr Zak said) to project it (using image seqence texture node) on a plane with transparency.


Add a plane and unwrap it. Download a fire animation from web (in my case I downloaded an explosion .avi file from here: http://wrathgames.com/blog/2011/12/25/explosion-animation-1/). Go to material nodes editor and set up the nodes as pictured below:


Set up the Emission node's strenght as you like. You might also use a Light Path node to get rid of the shadow casting by a projected movie clip.

To make the plane always face the camera (for the fly through animations  e.g.) use this solution: How can I make a plane always look at camera?